2. Cellular Respiration: Harvesting Energy from Glucose

3. Cellular respiration: Purpose

4. Exergonic and endergonic reactions of metabolism… Exergonic: C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O D G = -686 kcal/mole Cellular respiration! Endergonic: 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 D G = +686 kcal/mole Photosynthesis! Provides the energy to run cell processes Allows plants to make energy rich sugars from energy poor molecules

5. Summary of Cellular Respiration The 3 stages of cellular respiration… 1. Glycolysis: occurs in the cytoplasm of the cell results in the partial breakdown of glucose anaerobic – no oxygen is used during glycolysis

6. Summary of Cellular Respiration 2. Krebs Cycle occurs in the mitochondrial matrix aerobic – although O 2 is not used directly in this pathway, it will not occur unless enough is present in the cell. main catabolic pathway of C.R.

7. Summary of Cellular Respiration 3. Electron Transport Chain occurs along the inner mitochondrial membrane (IMM) aerobic – O 2 is used during this pathway. the main ATP producing pathway!

8. What happens during cellular respiration? The Big Picture! 1.The oxidation of food molecules (i.e. glucose) Stripping of high energy electrons (and H + ions) from food molecules. food is broken down via oxidation-reduction reactions (Redox reactions). Oxidation: Reduction: Whenever a molecule is oxidized, another molecule picks up the electrons and becomes reduced.

9. Just remember… LEO says GER!!!! loseelectronsoxidation gainelectronsreduction

10. 2. Electrons stripped from food molecules are accepted by electron carrier molecules (called NADH and FADH 2 ). The Big Picture (cont.) Food molecules are being oxidized, and the electron carriers are being reduced. Electrons stripped from food molecules have high potential energy. They are in a high energy shell!

11. Electron Carriers (The Big Picture cont.) 2 H + + 2 high energy electrons

12. Electron carriers (The Big Picture cont.)

13. 3. Electron carriers take these high energy electrons to the Electron Transport Chain. The Big Picture (cont.) Electrons are run down an “electron slide”… The energy released from this “slide” is used to make ATP… At the end of the slide, the electrons and H + are accepted by oxygen… …and become WATER!

14. C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O Oxidized! Reduced! e - and H +

16. Glycolysis The energy investment phase carbons ATP/NADH Ledger - 2 ATP Energy coupling ATP  ADP + P: exergonic Glu  Glu-6-P :endergonic

17. Glycolysis The energy payoff phase ATP/NADH Ledger -2ATP +2ATP +2 NADH Redox reactions Energy coupling

18. Glycolysis More energy coupling ATP/NADH Ledger -2ATP +2ATP +2 NADH End-products of glycolysis are 2 pyruvate molecules

19. Summary of Glycolysis Glucose activation: Energy Input = 2 ATP Energy Harvest = 4 ATP + 2NADH

20. Final Ledger -2ATP +2ATP +2 NADH What you need to know Final ledger for glycolysis Starting materials – one 6 carbon glucose molecule End products – two 3 carbon pyruvate molecules Don’t worry about all the intermediate molecules they are just there to illustrate what’s going on.

21. Each pyruvic acid molecule is broken down to form CO 2 and a two-carbon acetate molecule that binds to coenzyme A. This forms acetyl CoA, which enters the Krebs cycle. 1 NADH is produced here. Pyruvic acid must be chemically groomed to enter the Krebs cycle Figure 6.10 Pyruvic acid CO 2 Acetyl CoA (acetate and coenzyme A)

22. The Krebs cycle is a series of reactions in which enzymes strip away electrons and H + from each acetyl CoA molecule The Krebs cycle completes the oxidation of glucose, creating many NADH and FADH 2 molecules Figure 6.11A Acetyl CoA KREBS CYCLE 2 CO 2

23. Figure 6.11B Oxaloacetic acid Step Acetyl CoA stokes the furnace 1 2 carbons enter cycle Citric acid Steps and NADH, ATP,, and CO 2 are generated during redox reactions. 23 CO 2 leaves cycle Alpha-ketoglutaric acid CO 2 leaves cycle Succinic acid KREBS CYCLE Steps and Redox reactions generate FADH 2 and NADH. 45 Malic acid 1 2 3 4 5

24. What you must know about the Krebs Cycle Each turn requires one molecule of acetyl CoA. Don’t forget there are 2 turns per glucose molecule Each turn generates: –3 NADH molecules –1 ATP –1 FADH 2 molecule –Almost all of the energy removed from pyruvate molecules are carried by electron carrier molecules NADH and FADH 2 –Reaction intermediates (citric acid, oxaloacetate, etc.) are required to keep the cycle going.

25. Electron Transport Chain Electron carriers (NADH and FADH 2 ) take these high energy electrons to the Electron Transport Chain. Electrons are run down an “electron slide”… The energy released from this “slide” is used to make ATP… At the end of the slide, the electrons and H + are accepted by oxygen… …and become WATER!

26. Electron Transport results in H+ ions being concentrated in the intermembrane space Proton (H+) gradient is built up as a result of NADH (produced by Krebs cycle reactions) feeding electrons into electron transport system.

27. ATP Synthase enzymes use a proton (H+) gradient to put ADP and P together forming 32 ATP

28. Energy yield from Aerobic Cellular Respiration